Grave concerns have been raised about the sexual abuse of children in detention in the UK by independent experts at the United Nations.
Reviewing the UK's record, the United Nations Committee Against Torture cited a report into the abuse of some 1,000 children in custody from 2009-2017.
Few cases of such sexual abuse seem to have been investigated, the UN said.
The government said it would note the recommendations, adding that the UK had a tradition of protecting human rights.
The UN committee called on the UK to ensure all allegations of violence against children in detention were promptly and impartially investigated, adding that the information provided by the UK about the problem was insufficient.
It said historical claims of torture by security services in Northern Ireland must be addressed, too.
The committee also called for the age of criminal responsibility, currently 10 in England and Wales and 12 in Scotland, to be raised.
It added that the UK must report back on the abuse of children in custody and on Northern Ireland within a year.
The UN committee, which is meeting in Geneva, published its recommendations on Friday following the review.
In particular, it raised evidence from the UK's own Independent Inquiry into Child Sexual Abuse (IICSA) of the sexual abuse of more than 1,000 children in detention between 2009 to 2017.
Committee member and lead UN expert for the review of the UK Felice Gaer said the IICSA's report was "stunning in detail and in the horror that it sets forth".
The IICSA looked at young offender facilities, secure training centres and secure children's homes as part of a wider investigation into child abuse in England and Wales.
Many of the incidents involved staff inappropriately touching detainees during body searches or instances of restraint.
The Ministry of Justice (MoJ) said it was already conducting an urgent review into safeguarding in the youth estate following the IICSA.
In the last decade the number of children in youth custody has fallen by over 70%, it said.
Responding to the committee recommendations, an MoJ spokesperson added: "The UK has a longstanding tradition of ensuring rights and liberties are protected domestically and of fulfilling our international human rights obligations.
"We note the recommendations of the United Nations Committee Against Torture and will respond in due course."